1. Field of the Invention
The present invention relates to a cutting insert for chip-breaking metal machining being applicable for turning, milling and drilling. The cutting insert is normally made of coated or uncoated cemented carbide, but ceramic materials may also be used. It comprises an upper chip surface, a lower bottom surface, which is substantially plane parallel with the chip surface and which may be placed upon a cooperating bottom support surface of the holder, which for instance consists of a boring bar, a milling cutter body, an endmill or a drill. Further, the cutting insert comprises at least one side surface extending between said surfaces, which side surface has protruding portions according to claim 1.
2. Description of the Prior Art
Cutting inserts of cemented carbide for chip-breaking metal machining are conventionally shaped as so called indexable cutting inserts, i.e., one and the same cutting insert has two or more cutting edges, whereby it may be indexed when one cutting edge has worn out, so that a new unused cutting edge comes into operative engagement with the workpiece. The cutting insert is clamped in an insert seat in a holder, such as a milling cutter body or a boring bar. The most common way of clamping the insert is by a locking screw which is inserted through a through central aperture in the insert. However, other clamping arrangements do also occur, such as different clamps, central pins and lever pins. Inserts with a polygon basic shape, e.g., such as square, rectangular, triangular, rhombic and rhomboidic inserts, normally bear in an insert seat on one hand against a bottom support surface and on the other hand against two (exceptionally one) support surfaces, which bear against cooperating side surfaces of the insert. For square and rectangular inserts, said two support surfaces are normally perpendicular to each other, but, e.g., for triangular and hexagonal cutting inserts, the support surfaces normally have correspondingly other internal angles.
In order to be accomodated in an absolutely stable and fixed position, it is required that the support and side surfaces that bear against each other shall be entirely planar and that the support and side surfaces, respectively, have exactly the same internal angle. In practice, this has turned out to be very difficult to achieve and in principle this requires a careful grinding of both pairs of cooperating surfaces, which raises the production costs in a non-desirable way. In order to avoid this, it has been suggested to provide protruding support points or portions on the support surfaces, whereby only these then abut against the side surfaces of the insert, see for instance U.S. Pat. No. 5,443,334 (in particular FIG. 5). Of the same reason that a stool always stands firmly when it has three legs, the number of support points is three, which thus gives a statically well defined bearing (isostatic system). However, it is complicated and costly to shape the insert seat with such bearing points, inter alia because very small end mills have to be used.
Corresponding difficulties are also encountered for round cutting inserts. Thus, it is very difficult to attain two perfectly round surfaces with the same radius with an uninterrupted bearing along a large circle sector. Therefore, also in this case one normally shapes the round support surface of the insert seat with two bearing points, against which the round side surface of the insert bears in an isostatic way. Also in this case, corresponding difficulties arise to produce the round support surface of the insert seat.